With the development of communications technologies, more mobile services occur indoors nowadays. According to statistics, it is found that voice services that occur indoors account for nearly 70% of voice services in a communications network system, and traffic of data services that occur indoors accounts for nearly 90% of total traffic of data services in the communications network system.
Currently, newly added UMTS (Universal Mobile Telecommunications System) and LTE (Long Term Evolution) are basically deployed on a 2 GHz frequency band (it should be noted that, compared with 900 Hz, 2 GHz belongs to a high frequency band signal). However, a high frequency band signal has a weaker penetrability than a low frequency band signal; as a result, newly established 3G and 4G networks have a problem that quality of indoor signal coverage is low within a deployment range, and therefore, an indoor requirement cannot be met.
Based on the foregoing situation, an indoor signal coverage technology emerges. Common indoor signal coverage systems are generally classified into an active indoor signal coverage system and a passive indoor signal coverage system.
A typical active indoor signal coverage system is an iDBS (indoor distributed base station) system; and a typical passive indoor signal coverage system is a DAS (distributed antenna system).
The DAS includes a BBU (baseband unit), an RRU (remote radio unit), a combiner, an antenna device, and the like. A working principle of the DAS is that: after the BBU sends a signal to the RRU and the RRU converts the signal into a radio frequency signal, the radio frequency signal is led into a room by using a transmission device such as a radio frequency feeder, a combiner/splitter, or an antenna. In the DAS system, after the splitter performs splitting processing on the radio frequency signal processed by the RRU, the radio frequency signal is distributed to an indoor user equipment by using the antenna device; and after a feedback signal passes through the combiner and undergoes simple superposition, the indoor user equipment transmits the feedback signal to the RRU by using the radio frequency feeder. It can be seen that, in the DAS, a signal is processed by using a combiner/splitter. Although the working principle is simple, relatively high system noise, a small signal transmission capacity, and relatively poor indoor signal quality are easily caused.
However, the iDBS system uses a three-layer structure: BBU-RHUB (RRU Hub, remote radio unit hub)-RRU. One BBU may be connected to multiple RHUBs, and each RHUB may be connected to multiple RRUs. An RHUB and an RRU are connected by using a network cable, where the network cable mainly completes signal distribution and aggregation, and supplies power to the RRU; and functions of the BBU and the RRU are the same as those of the BBU and the RRU in the DAS system.
Use of an RHUB device in the iDBS system avoids problems of relatively high system noise and relatively poor indoor signal quality that are caused by a combiner/splitter; however, because a structure of an indoor signal coverage system constructed by using RHUB devices in the iDBS system is simple, an extension capability of the indoor signal coverage system is restricted, and a capacity requirement of a data service burst for the indoor signal coverage system cannot be met.